1. Field of the Invention
The present invention relates generally to an apparatus and method for solving congestion in a Wideband Code Division Multiple Access (WCDMA), and in particular, to an apparatus and method for solving congestion in a WCDMA system by switching the service cell mode of mobile communication terminals belonging to both a WCDMA cell and a Global System for Mobile Communication (GSM)/General Packet Radio Services (GPRS) cell among mobile communication terminals into the GSM/GPRS cell, upon a request for a circuit service, when congestion occurs in a base station of the WCDMA system.
2. Description of the Related Art
Current mobile communication systems have advanced beyond the initial speech-based service, and now provide high-speed and high-quality radio data packet communication systems for data and multimedia services. Particularly, a Universal Mobile Telecommunication Service (UMTS) system, which is the third-generation (3G) mobile communication system, is constructed based on GSM and GPRS, which are European mobile communication systems, and adopts WCDMA technology. The UMTS system provides a consistent service of transmitting packet-based texts, digital speech data, video data and/or multimedia data at a transmission rate of over 2 Mbps to users of mobile phones or computers, regardless of user location.
The UMTS system is composed of a Core Network (CN) and a plurality of Radio Network Subsystems (RNS). The RNSs constitute a UMTS Terrestrial Radio Access Network (UTRAN). Each of the RNSs is composed of a Radio Network Controller (RNC) and a plurality of base stations, i.e., node B. The RNCs are divided into a Serving RNC (SRNC), a Drift RNC (DRNC) and a Control RNC (CRNC) according to their role. The serving RNC manages information of a User Equipment (UE) and transmits/receives data to/from the core network. The drift RNC directly and wirelessly accesses the user equipment. The control RNC controls radio resources of each node B.
The RNCs allocate radio resources to a plurality of node Bs that they manage, and the node Bs substantially provide the allocated radio resources from the RNCs to UEs. The radio resources provided by each node B are formed for each cell and signify radio resources of a particular cell managed by the corresponding node B. The UE sets up a radio channel based on the radio resources of the particular cell managed by the node B, and transmits/receives data through the established radio channel. Since the UE recognizes only a physical channel formed for each cell, it is meaningless to distinguish a node B from a cell. Therefore, the terms node B and cell will be used interchangeably and have the same meaning in the present specification.
Meanwhile, there are many regions where a WCDMA cell is overlapped with a GSM/GPRS cell in a downtown area. When congestion occurs, a WCDMA node B passes over a mobile communication terminal caught in the middle of speech communication in the overlapped region into the GSM/GPRS cell by performing handover, and a conventional WCDMA node B passes over a mobile communication terminal into a GSM/GPRS cell through cell reselection. When a user uses a speech service after the cell switching, there is no difference in the quality of service whether the mobile communication belongs to the WCDMA cell or the GSM/GPRS cell. However, when the user uses a packet service such as the Internet, the user cannot receive the high-speed packet service, which is the advantage of the WCDMA system.
Accordingly, there is needed an apparatus and method for switching the service cell mode of a mobile communication terminal from a WCDMA cell into a GSM/GPRS cell according to the type of service requested by the user, when congestion occurs in the WCDMA node B.